User`s guide

Chapter 3 Managing the Barracuda Spam Firewall ■ 55
Preventing Dictionary Attacks Using Barracuda MS Exchange Accelerator
3. Click Save Changes.
Preventing Dictionary Attacks Using Barracuda MS Exchange Accelerator
A "Dictionary" or NDR (Non-Delivery Report) attack occurs when a spammer tries to delivery a series
of messages to every possible recipient name on an email server.
Microsoft Exchange attempts to protect against dictionary attacks by accepting messages for all
recipients rather than rejecting invalid recipients and letting a spam sender know which accounts are
valid. Unfortunately, this often causes the Exchange server to experience a high CPU load because the
server still attempts to send one or more non-delivery notifications for every invalid recipient.
The Barracuda MS Exchange Accelerator feature uses the LDAP service built into Exchange to verify
recipients before delivering messages to the MS Exchange server and consuming valuable resources. If
the recipient cannot be verified, the Barracuda Spam Firewall does not deliver the message. This
premium service is recommended for all MS Exchange configurations.
Note: The LDAP protocol must be enabled on your Exchange server in order to use the Barracuda MS
Exchange Accelerator. LDAP is automatically on by default in most MS Exchange installations.
To set up the Barracuda MS Exchange Accelerator service:
1. Go to the DOMAINS-->Domain Manager page.
2. Click Edit LDAP in the Actions column.
Realm Name The name of the realm as displayed to users in the Realm Selector as well
as in the Domain Settings for administrators.
A realm is a database of usernames and passwords that identify valid
users, plus the list of roles associated with each valid user.
Tag Score, Quarantine
Score, Block Score
For information on spam scoring, refer to Configuring the Global Spam
Scoring Limits on page 28.
Per-User Quarantine Determines the quarantine type for the domain. Selecting Yes sets the
quarantine type to Per-User. Selecting No sets the quarantine type to
Global. For information on quarantine types, refer to Specifying the
Quarantine Type on page 30.
Global Quarantine
Email Address
Specifies the address for the global quarantine email address for the
domain. For more information, refer to Specifying the Global Quarantine
Settings on page 30.
Spam Scan Enabled,
Virus Scan Enabled
Lets you enable or disable spam and virus checking for the domain.
Spoof Protection Whether the Barracuda Spam Firewall prevents outside individuals from
sending mail using your domains as the “from” address. Setting this option
to Yes blocks all mail addressed from a domain for which the Barracuda
Spam Firewall receives mail.
You should only enable this option if all mail from your domains goes
directly to your mail server and not through the Barracuda Spam Firewall.
Setting Description